Conventional axial piston variable displacement hydraulic units include a cylinder block rotatably supported in a main housing with a plurality of axial cylinders arranged in an annular pattern, a swash plate supported in the main housing controls for tilting the swash plate, an end cap on the housing which contains the high pressure porting, and a front cover on the housing with a mounting flange. In many cases, the main housing consists of forward and rearward halves which are joined along a central flange, so that the various components of the hydraulic unit may be easily installed during assembly. However multiple-component housings for such hydraulic units suffer several problems.
First, seals are required at the joints of the housing components for hydraulic passage between the components. Leakage at such seals is a common problem since large hydraulic loads are created axially along the input shaft, which act directly on the various joints between the housing components.
Second, to restrain the housing components against the separation forces caused by these hydraulic thrust loads, various fastening systems are required along all such joints. These fastening systems take up large amounts of space, and thereby require a housing which is larger than is specifically needed for the hydraulic apparatus. Larger hydraulic units require more materials and greater space in the vehicle or apparatus in which the unit is used.
Because of these space limitations, components such as valves and controls must be designed to fit within one of the separate housing components. This severely restricts the design and location of such components.
In addition, since prior art housings have joints in the path of the major hydraulic separating force, the locations of various access ports are generally limited to the end plate or front plate of the housing.
It is therefore a general object of the present invention to provide an improved housing for hydraulic units.
A further object is to provide a unitary hydraulic housing unit which eliminates housing component joints along the path of major hydraulic separating forces.
Still another object of the present invention is to provide a unitary hydraulic housing unit with access openings oriented transversely to the axially directed hydraulic forces within the housing unit.
These and other objects will be apparent to those skilled in the art.